The present invention relates to the deicing of air inlet cowls of jet engines, particularly aircraft engines.
It is known that, if necessary (as a preventative measure against the formation of ice or to eliminate ice already formed), the leading edge of the air inlet cowl of such engines is deiced by heating it with pressurized hot air tapped from said engine and supplied to said leading edge by a hot air circulation circuit.
To this end, an air inlet cowl such as this comprises:
a hollow leading edge delimiting an internal peripheral chamber closed by an internal partition (or frame) and equipped with orifices placing said internal chamber in communication with the outside; and
a pipe which can be connected, at its rear end which is the opposite end to said leading edge, to said hot air circulation circuit and, at its front end toward the leading edge, to an injector injecting said hot air into said internal chamber.
Thus, the pressurized hot air injected by said injector sweeps through said internal peripheral chamber, heating it up, and is discharged through said orifices.
U.S. Pat. No. 5,365,731 already discloses an air inlet cowl of this type comprising a number of such hot air discharge orifices made directly in the leading edge of said cowl, the rate of flow of the deicing hot air being controlled by the cross section of said orifices. A known air inlet cowl such as this has the major drawbacks of weakening the leading edge of said cowl (which happens to be the most vulnerable part of an engine nacelle, because it is located at the front, and to be difficult to repair because of its large size) and of substantially degrading the aerodynamic performance of said cowl. Specifically, as far as the latter drawback is concerned, this is because said orifices are located in a shape of leading edge that encourages scooping xe2x80x94 and therefore makes the ejection of hot air difficult xe2x80x94 this being true throughout all the phases of flight of the aircraft when the deicing is not in operation. In addition, the ejection orifices produce a large ejection area, which leads to drag over a high proportion of the leading edge, this drag being accentuated by the fact that the surface of the nacelle immediately downstream of this aerodynamically polluted surface, is also generally very disturbed, which means that it generates additional drag. Furthermore, in a known air inlet cowl such as this, it is difficult to correct the ejection cross section during flight trials, because this section consists of orifices made in a very large part (the leading edge).
Another source, document EP-A-0 205 283, discloses an air inlet cowl in which said pressurized hot air supply pipe is surrounded by an enveloping metallic structure comprising pipework, the free end of which forms an orifice used for ejecting deicing air to the rear of the leading edge of said cowl. This then avoids the aforementioned drawbacks but, in this known device, the rate of flow of hot air is controlled by the cross section of said ejection pipework, as well as by the orientation of fins located at the free end thereof. This results in poor control over the ejection rate and in layers of hot air on the outside. In addition, the ejection of the hot air is highly concentrated, which may damage nearby structures which are sensitive to heat. In any case, a device such as this is the source of significant thermal radiation, also with the risk of damaging said structures. Finally, the device is expensive because it consists of many parts which have to be assembled using joints whose life is limited because they are subjected to high temperatures.
Also known, for example from document GB-A-2 259 679 , is an air inlet cowl in which the deicing hot air is discharged to the outside by bent pipework passing through said internal partition to eject the hot air at the rear of said leading edge. Here again, the rate of flow of hot air is controlled by the cross section of the pipework and by the orientation of fins arranged therein. This air inlet cowl therefore again encounters the same drawbacks as those mentioned hereinabove with regard to document EP-A-0 205 283.
Finally, document EP-A-0 536 089 discloses an air inlet cowl in which said internal partition is equipped with a trough-shaped duct directed toward the rear of the leading edge and open toward the periphery of said air inlet cowl. The trough-shaped duct is closed off by a plate pierced with a multitude of identical rectangular orifices, whose direction is orthogonal to the leading edge, said orifices being aligned parallel to the latter.
By virtue of this arrangement, said orifices, which serve to discharge to the outside the pressurized hot air which has heated up said leading edge, may be in the part of said cowl that is located just behind said leading edge. This therefore means that the leading edge, which is a part which is sensitive from the aerodynamic point of view in terms of engine performance and from the maintenance point of view because it is exposed to various impacts, is not weakened by said orifices. However, an arrangement such as this does not make it possible to optimize the ejection of the deicing hot air either aerodynamically or thermally or acoustically, particularly because:
the jets of hot air passing through said rectangular orifices tend to group together downstream of said plate, which gives rise to significant aerodynamic drag and detracts from the cooling of said jets (the thermal radiation of which thus runs a risk of burning the outer surface xe2x80x94 generally made of composite material xe2x80x94 of said cowl downstream of said plate); and
the jets of hot air passing through the lateral rectangular orifices widen laterally and burn the lateral surface, also made of composite material, of said cowl, which surface is located laterally to said plate.
Furthermore, such orifices give rise to aerodynamic noise, whistling, etc.
The object of the present invention is to overcome these drawbacks.
To this end, according to the invention, the air inlet cowl for a jet engine, particularly for an aircraft, said air inlet cowl being equipped, at the front, with means for deicing its leading edge and for this purpose comprising:
a hollow leading edge delimiting an internal peripheral chamber which is closed by an internal partition, said internal partition being equipped with a trough-shaped duct directed toward the rear of said leading edge and open toward the periphery of said air inlet cowl;
a pipe which can be connected, at its rear end which is the opposite end to said leading edge, to a pressurized hot air circuit and, at its front end toward said leading edge, to an injector injecting said pressurized hot air into said internal chamber; and
a calibration piece made of a material resistant to high temperatures and forming part of the external surface of said cowl, to the rear of said leading edge, said piece closing off said trough-shaped duct and being pierced with orifices to place said internal chamber in communication with the outside, said orifices being distributed at least roughly parallel to said leading edge and serving to calibrate the flow of pressurized hot air ejected by said trough-shaped duct, while deflecting away from said cowl the pressurized hot air jets resulting from the passage of said flow of hot air through said orifices, is noteworthy in that said orifices form an arrangement such that at least two pressurized hot air jets passing through two adjacent orifices have, downstream of said calibration piece, different inclinations with respect to said calibration piece, and in that said calibration piece extends longitudinally in said external surface of said cowl, toward the rear thereof, to act as thermal protection for said cowl with respect to said hot air jets passing through said orifices.
Thus, said orifices allow control over the rate of ejection and, also, make it possible to obtain favorable heat exchange between the ejected hot air and the external ambient air while at the same time controlling the spread of the hot air jet in order to keep it away from the temperature-sensitive structures of the nacelle. This then avoids the drawbacks of the orifices of the known deicing devices which:
when they are in the form of a circular orifice, excessively concentrate the ejection cross section and afford a small area for heat exchange between the jet of deicing air and the ambient external air, the energy of said jet being too great which means that it risks reaching the temperature-sensitive structures and damaging them; and
when they are spread, as a multitude of orifices, give rise to acoustic emissions, aerodynamic drag prejudicial to aircraft performance, even when the deicing circuit is not in operation, and the risk of burning the cowl around said orifices.
It will in fact be noted that, by virtue of the differences in inclination of said hot air jets with respect to said calibration piece, the fresh aerodynamic flow can very easily penetrate between these jets, cooling them efficiently and avoiding, or at the very least reducing, the generation of parasitic drag and acoustic noise.
It will also be noted that, by virtue of the invention, the longitudinal extension of said calibration piece can be chosen so that the heating of the external surface of the cowl, downstream of said piece as a result of the thermal radiation of said hot air jets, remains below a given temperature threshold capable of avoiding thermal damage to said surface.
In one particular embodiment, said orifices form an arrangement such that, in addition, at least one pressurized hot air jet passing through an orifice (lateral or otherwise) of said calibration piece is absorbed, downstream of this piece, by at least one pressurized hot air jet passing through an orifice occupying an adjacent position, for example a less lateral position, in said calibration piece.
Furthermore, in an advantageous embodiment, in which said orifices have an oblong shape and are oriented at least approximately longitudinally, that is to say from the front of the cowl to the rear, the area of each orifice depends on the position of this orifice in said arrangement, this area varying according to how laterally positioned said orifice is. As a preference, the area is all the smaller the more lateral the position of the orifice, and all the greater the more central the position of said orifice, although the reverse is, however, equally possible.
By virtue of this arrangement, the energy of a hot air jet is all the greater the greater the area of the corresponding orifice, so that:
the inclination of a hot air jet with respect to said calibration piece depends on the area of the orifice through which said jet passes, a jet corresponding to an orifice of larger area being kept further away from the surface of the cowl than a jet corresponding to an orifice of smaller area; and
the air jets of lower energy, particularly the lateral hot air jets, can be absorbed by the jets of higher energy.
The front edges of said orifices of the arrangement may be at least roughly aligned parallel to said leading edge and said orifices may have an at least roughly rectangular shape.
Furthermore, to optimize the penetration of the aerodynamic flow between said jets and therefore optimize the heat exchange between said flow and these jets, it is advantageous for each oblong orifice to be oriented at least roughly parallel to the stream lines of said aerodynamic flow flowing over said calibration piece, for example when the aircraft is in cruising flight.
In one particularly simple and effective embodiment of the cowl according to the present invention, said arrangement of orifices comprises at least one large central orifice, two small lateral orifices arranged on each side of said central orifice and two intermediate orifices, the area and position of which are respectively between those of said large central orifice and those of said small lateral orifices.
It will be noted that the number of orifices depends on the dimensions of the calibration piece. Specifically, the shorter this piece, the greater the efficiency of the heat exchanger (consisting of the orifices) will have to be. It may therefore be necessary to vary the number of orifices in order to obtain the desired effect. Conversely, the longer the calibration piece, the more the number of orifices can be reduced, the quality of the heat exchanger being less of an important issue here.
Of course, in the context of the present invention, the total number of orifices may be even or odd. However, as a preference, said number of orifices is an odd number. This in particular makes it possible to improve the efficiency because the lateral jets then, through a lift effect, play a part in lifting the central jet.
Moreover and advantageously, said arrangement of orifices is symmetrical, preferably with respect to a longitudinal plane which, in the case of an odd number of orifices, passes through the central orifice and, in the case of an even number, passes mid-way between the two central orifices.
In order to optimize the thermal protection afforded by said calibration piece while at the same time minimizing its mass, it is advantageous for at least one of the longitudinal edges of said calibration piece to have the shape of the stream lines of the aerodynamic flow flowing over said calibration piece when the aircraft is in cruising flight.
As a preference, said trough-shaped duct is peripherally in the vicinity of said pressurized hot air supply pipe. Thus, said hot air sweeps through the entire circumference of said leading edge and very uniform distribution of said hot air inside the latter, and therefore very good deicing performance, are obtained.
Said calibration piece may in addition form the inspection hatch for said hot air supply pipe. Benefit can therefore be derived from the presence, compulsory for access to the deicing air pipework, of a dismantleable and high-temperature-resistant panel located immediately behind said ejection orifices. As mentioned above, such a hatch may extend longitudinally in the external surface of the cowl over sufficient length to protect the entire part of that surface which may be subjected to the action of the flow of hot air ejected by said orifices. In addition, by providing several dismantleable panels equipped with different ejection orifice arrangements, one panel can easily be replaced with another to test various ejection orifice arrangements.
Furthermore, it is advantageous for said trough-shaped duct to widen toward the external periphery of said cowl. It may thus have an aerodynamic shape that encourages the ejection of air.
Said trough-shaped duct may form an integral part of said internal partition and, for example, be formed by pressing the latter. It may also constitute a piece attached to said internal partition, in a recess thereof.
It can thus be seen that the leading edge of the cowl according to the present invention is homogeneous over all 360xc2x0 of its circumference, without protrusions or vent orifices, thus preserving its aerodynamic and mechanical strength qualities.